In the field of computer networking, many efforts have been made to determine the best way for servers within a computer network to communicate with one another. In particular, the problem of which network links to use has been a challenge. While there may be a dozen paths that communication between two computers may use, only one or two of those paths may actually be the best. In making this determination, a network engineer may have a set of parameters to follow. These parameters may include: minimizing the distance that communications need to travel, maximizing the bandwidth available for each communication, or minimizing the amount of money spent creating the links between the computers. Such parameters will hereinafter be grouped under the general category of “cost.” In other words, a network engineer tries to minimize the cost of sending messages between computers in a network. The “cost” of a network link as used herein may include, but is not limited to, one or more of the following: the time it takes for data to travel over the link, the physical length of the link, or the monetary cost of the link. Thus, if travel time is being used as a parameter, then a “cheap” link is one that is relatively fast, whereas an “expensive” link is relatively slow.
Several techniques have been developed to create minimum-cost network topologies. However, many of these techniques become unworkable when the problem of intermediate servers is introduced into a network. Intermediate servers are those servers that co-exist in a network with the servers for which communication is being optimized, but are not the intended recipients of the message. Those servers that are the intended recipients will be referred to herein as “recipient servers.”
For example, servers on computer networks may share what is known as a “multi-master” or “distributed” database, in which multiple servers share responsibility for keeping the contents of the database current. An example of such a database is the MICROSOFT ACTIVE DIRECTORY SERVICE. Copies of parts or all of a shared database may be stored on several servers. When one server makes a change to a portion of the database, that change needs to be transmitted to all of the other servers that possess copies of that portion. Transmitting database changes from one server to another is also known as “replicating” the changes. Replication among the various servers of a network takes place according to an established pattern or “replication topology.” Those servers that share the responsibility for maintaining the shared database will be referred to herein as “replicating servers.” A replicating server is one implementation of a “recipient server.”
There are many situations in which a network may have both replicating servers and intermediate servers. One such situation is when a shared database is divided into several partitions, in which a server may only exchange database updates with another server in the same partition. For example, a corporate directory may be divided into sales, development and marketing partitions, such that sales servers only replicate with other sales servers, development servers only replicate with other development servers, and marketing servers only replicate with other marketing servers. In such a network, dissimilar servers would be seen as intermediate servers with respect to one another. For example, marketing servers and development servers would be seen as intermediate servers by the sales servers, since sales data would not be replicated by the other two types of servers, but would simply be passed through. Data replicated between recipient servers may have to pass through these intermediate servers, and therefore they may need to be considered when determining a minimum-cost replication scheme.
Thus it can be seen that there is a need for a new method for designating communication paths in a computer network.